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From: Peter Zijlstra <peterz@infradead.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Qian Cai <cai@redhat.com>,
	Vincent Donnefort <vincent.donnefort@arm.com>,
	Dexuan Cui <decui@microsoft.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU
Date: Thu, 14 Jan 2021 14:12:03 +0100	[thread overview]
Message-ID: <YABDI6Qkp5PNslUS@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJhGHyD_xuSpYOp5A9PumWGsBA=DNqM0ge3_NgRkfro7fafGqA@mail.gmail.com>

On Wed, Jan 13, 2021 at 09:28:13PM +0800, Lai Jiangshan wrote:
> On Tue, Jan 12, 2021 at 10:51 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > @@ -4972,9 +4977,11 @@ static void rebind_workers(struct worker
> >          * of all workers first and then clear UNBOUND.  As we're called
> >          * from CPU_ONLINE, the following shouldn't fail.
> >          */
> > -       for_each_pool_worker(worker, pool)
> > +       for_each_pool_worker(worker, pool) {
> >                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
> >                                                   pool->attrs->cpumask) < 0);
> > +               kthread_set_per_cpu(worker->task, true);
> 
> Will the schedule break affinity in the middle of these two lines due to
> patch4 allowing it and result in Paul's reported splat.

So something like the below _should_ work, except i'm seeing odd WARNs.
I'll prod at it some more.

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2371,6 +2371,7 @@ static int worker_thread(void *__worker)
 	/* tell the scheduler that this is a workqueue worker */
 	set_pf_worker(true);
 woke_up:
+	kthread_parkme();
 	raw_spin_lock_irq(&pool->lock);
 
 	/* am I supposed to die? */
@@ -2428,6 +2429,7 @@ static int worker_thread(void *__worker)
 			move_linked_works(work, &worker->scheduled, NULL);
 			process_scheduled_works(worker);
 		}
+		kthread_parkme();
 	} while (keep_working(pool));
 
 	worker_set_flags(worker, WORKER_PREP);
@@ -4978,9 +4980,9 @@ static void rebind_workers(struct worker
 	 * from CPU_ONLINE, the following shouldn't fail.
 	 */
 	for_each_pool_worker(worker, pool) {
-		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
-						  pool->attrs->cpumask) < 0);
+		kthread_park(worker->task);
 		kthread_set_per_cpu(worker->task, true);
+		kthread_unpark(worker->task);
 	}
 
 	raw_spin_lock_irq(&pool->lock);

  parent reply	other threads:[~2021-01-14 13:13 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-12 14:43 [PATCH 0/4] sched: Fix hot-unplug regressions Peter Zijlstra
2021-01-12 14:43 ` [PATCH 2/4] kthread: Extract KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-12 14:43 ` [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-12 16:36   ` Lai Jiangshan
2021-01-13 11:43     ` Peter Zijlstra
2021-01-12 17:57   ` Valentin Schneider
2021-01-13 13:28   ` Lai Jiangshan
2021-01-13 14:16     ` Valentin Schneider
2021-01-13 17:52       ` Paul E. McKenney
2021-01-13 18:43         ` Valentin Schneider
2021-01-13 18:59           ` Paul E. McKenney
2021-01-14 13:12     ` Peter Zijlstra [this message]
2021-01-14 13:21       ` Valentin Schneider
2021-01-14 15:34         ` Peter Zijlstra
2021-01-16  6:27           ` Lai Jiangshan
2021-01-16 12:45             ` Peter Zijlstra
2021-01-16 14:45               ` Lai Jiangshan
2021-01-16 15:16                 ` Peter Zijlstra
2021-01-16 16:14                   ` Lai Jiangshan
2021-01-16 18:46                     ` Peter Zijlstra
2021-01-17  9:54                       ` Peter Zijlstra
2021-01-16 15:13               ` Peter Zijlstra
2021-01-12 14:43 ` [PATCH 4/4] sched: Fix CPU hotplug / tighten is_per_cpu_kthread() Peter Zijlstra

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